Back to EveryPatent.com
United States Patent |
6,101,172
|
van Bavel
,   et al.
|
August 8, 2000
|
Transmission spectra for HDSL2 transmission
Abstract
A PSD template for an HDSL2 transmission system includes three regions, a
full-duplex region for both upstream and downstream transmission, and two
half-duplex regions, a first duplex region for containing substantially
upstream power and a half-duplex region for containing substantially
downstream power.
Inventors:
|
van Bavel; Nicholas (4208 Avenue H, Austin, TX 78751);
McCaslin; Shawn (505 Leisurewoods Dr., Buda, TX 78610)
|
Appl. No.:
|
934405 |
Filed:
|
September 19, 1997 |
Current U.S. Class: |
370/295; 370/480 |
Intern'l Class: |
H04J 001/18 |
Field of Search: |
370/295,296,480,482,489,490,493-495
|
References Cited
Other References
Performance and Spectral Compatibility of OPTIS HDSL2, T1E1.4/97-237, pp.
3-7, undated.
A Modulation Technique for CSA Range HDSL2, Schneider, K. and Goodson, R.,
T1E1.4/97-073, pp. 1-9, Feb. 1997.
Refined HDSL2 Transmission Masks: Performance & Compatibility, Rude, M.,
T1E1.4/94-170, pp. 1-6, May 1997.
Performance and Spectral Compatibility Comparison of POET PAM and
OverCAPped Transmission for HDSL2, Zimmerman, G., T1E1.4/97-179, pp. 1-5,
May 1997.
HDSL2 Transmit Spectra, Liu, J. and Zimmerman G., T1E1.4/97-178, pp. 1-5,
May 1997.
Evaluation of the Performance of the POET System, Takatori, H.,
T1E1.4/97-191, pp. 1-5, May 1997.
Spectral Shaped Transmission for HDSL2, Takatori, H., T1E1.4/97-192, pp.
1-9, May 1997.
A Proposal for HDSL2 Transmission: OPTIS, Rude, M., Sorbara, M., Takatori,
H. and Zimmerman, G., T1E14/97-238, pp. 1-3, Jun./Jul. 1997.
OPTIS PSD Mask and Power Specification for HDSL2, Girardeau, J., Takatori,
H., Rude, M. and Zimmerman, G., T1E14/97-320, pp. 1-14, Sep. 22, 1997.
Zimmerman, G.A., "Achievable rates vs. Operating Characterstics of Local
Loop Transmission: HDSL, HDSL2, ADSL and VDSL", Signals, Systems &
Computers, 1997, IEEE Cat. No. 97CB36136, pp. 573-577, Nov. 1997.
|
Primary Examiner: Marcelo; Melvin
Attorney, Agent or Firm: Howison; Gregory M.
Claims
What is claimed is:
1. The system for transmitting PAM data between upstream and downstream
locations on a twisted pair and a frequency division multiplexed system,
comprising:
a transmitter disposed at each of the upstream and downstream locations for
transmitting data over the twisted pair;
a receiver disposed at each of the upstream and downstream locations for
receiving data from the twisted pair;
said transmitter and receiver transmitting and receiving data with defined
frequency spectra which is shaped at said respective transmitter and
receiver, a downstream spectra associated with transmissions from the
upstream location to the downstream location, and an upstream spectra
associated with transmissions from the downstream location to the upstream
location, each of the upstream and downstream spectra divided into three
common regions, a full-duplex region, a first half-duplex region, and a
second half-duplex region, wherein:
said upstream and downstream spectra sharing said full-duplex regions,
which said full-duplex regions each extend from DC to a first frequency,
said upstream spectra associated substantially with said second half-duplex
region to pass signal therethrough and substantially reject signal in said
first half-duplex region,
said downstream spectra associated substantially with said first
half-duplex region to pass signal therethrough and substantially reject
signal in said second half-duplex region, and
said first and second half-duplex regions disposed adjacent each other.
2. The system of claim 1 wherein said first and second half-duplex regions
are symmetrical about each other.
3. The system of claim 2 wherein said first and second half-duplex regions
are adjacent to each other and symmetrical about f.sub.baud /2.
4. The system of claim 1 wherein said full-duplex region is disposed
substantially adjacent to said first half-duplex region.
5. The system of claim 1 wherein said full-duplex region associated with
said upstream spectra has less attenuation than said full-duplex region
associated with said downstream spectra.
6. The system of claim 1 wherein the amplitude of said second half-duplex
region for said upstream spectrum is substantially equal to the amplitude
of said first half-duplex region for said downstream spectrum.
7. The system of claim 1 wherein the amplitudes of said second half-duplex
region in said upstream spectra and the amplitude of said downstream
spectra in said first half-duplex region are greater than the amplitudes
of said upstream and downstream spectra in said full-duplex region.
Description
TECHNICAL FIELD OF THE INVENTION
The present invention pertains in general to transmitting information over
HDSL2 communication links and, more particularly, to the transmission
spectrum therefor.
BACKGROUND OF THE INVENTION
In transmitting data over a twisted pair, there have been proposed a number
of different techniques, especially those for generating line codes for
transmission systems, such as two-loop HDSL. The line codes that have been
utilized have included echo-canceled and FDM versions of QAM/CAP, PAM, and
DMT. These are all provided in various T1E1 contributions. However, one of
the benchmarks for transmission over the two-loop HDSL is referred to as
the 6 dB margin CSA (carrier serving area) range. Some of the techniques
are described in K. Schneider, "A Modulation Technique for CSA Range
HDSL2," HDSL Study Project for T1E1.4 Technical Subcommittee Working Group
Members, Feb. 3-7, 1997, which is incorporated herein by reference.
Although substantially all of the modulation methods for CSA have fallen
short of the 6 dB range, they have been combined with various
encoding/decoding techniques to increase their range. One such modulation
method is the Overlapped PAM Transmission with Interlocking Spectra
(OPTIS), this being a modulation method for CSA range HDSL2 transmission.
This proposed approach has purported to achieve an uncoded SNR margin in
excess of 1 dB for all provisionally agreed crosstalk environments, as
well as mixed crosstalk scenarios. This is combined with a 5 dB forward
error correction code, a trellis code, to provide an overall 6 dB of coded
performance margin on CSA loops. However, it is very difficult to achieve
the 5 dB forward error correction code, even with a trellis technique. It
is relatively easy to achieve 4 dB forward error correction, but an
additional 1 dB is considerably more difficult. Therefore, the 1 dB
uncoded SNR margin is marginal at best when realizing the difficulty of
achieving the 5 dB for error correction improvement. The OPTIS technique
is described in M. Rude, M. Sorbara, H. Takatori, and G. Zimmerman, "A
Proposal for HDSL2 Transmission: OPTIS" Standards Project: T1E1.4:HDSL2,
Jun. 30-Jul. 2, 1997, which is incorporated herein by reference.
The OPTIS transmission technique utilizes an iteratively determined HDSL2
transmit spectrum, one for the downstream data, and one for the upstream
data. It is noted that the transmit spectra is defined as a set of
"templates" which are basically filters that define the frequency
spectrum. By so shaping the frequency spectrum, the desired transmission
technique can be achieved. However, as noted above, even the 1 dB uncoded
SNR is marginal at best when considering that the benchmark is a 6 dB CSA
range.
When a communication system utilizing twisted pair loops is implemented, it
must be realized that a plurality of these loops with be "bundled" with
each other. There can therefore exist crosstalk between systems that
operate on identical transmission mode, and there can be additional
problems when there are two different transmission modes that are being
transmitted down twisted pairs in the same line. In any event, if the
crosstalk from adjacent lines within a bundle presents a noise error to
the system, this will decrease the SNR of the system. Therefore, various
techniques have been implemented that will reduce the input of crosstalk.
SUMMARY OF THE INVENTION
The present invention disclosed and claimed herein comprises a system for
transmitting PAM data between upstream and downstream locations on a
twisted pair in a frequency division multiplexed system. The system
includes a transmitter disposed at each of the upstream and downstream
locations for transmitting data over the twisted pair and a receiver
disposed at each of the upstream and downstream locations for receiving
data from the twisted pair. The transmitter and receiver both transmit and
receive data with defined frequency spectra, which spectra is shaped at
said respective transmitter and receiver. The frequency spectra is
comprised of a downstream spectra associated with transmissions from the
upstream location and an upstream spectra associated with transmissions
from the downstream location to the upstream location. Each of the
upstream and downstream spectra are divided into three regions, a
full-duplex region, a first half-duplex region and a second half-duplex
region. The upstream and downstream spectra both share the full-duplex
regions of the respective spectra, which full-duplex regions extend from
DC to the first frequency. The upstream spectra is associated
substantially with the second half-duplex region to pass signals
therethrough and substantially reject signals in the first half-duplex
region. The downstream spectra is associated substantially with the first
half-duplex region to pass signals therethrough and substantially reject
signals in the second half-duplex region. The first and second half-duplex
regions are disposed adjacent each other.
In another aspect of the present invention, the first and second
half-duplex regions are symmetrical about each other. They are also
disposed symmetrical about f.sub.baud /2, wherein the baud rate is three
times the Nyquist sampling rate.
BRIEF DESCRIPTION OF THE DRAWINGS
For a more complete understanding of the present invention and the
advantages thereof, reference is now made to the following description
taken in conjunction with the accompanying Drawings in which:
FIG. 1 illustrates a block diagram of overall transmission systems for
transmitting over a given HDSL2 loop;
FIG. 2 illustrates a prior art template for the OPTIS technique; and
FIG. 3 illustrates the template for the preferred embodiment of the present
invention.
DETAILED DESCRIPTION OF THE INVENTION
Referring now to FIG. 1, there is illustrated a block diagram of a
transmission system for transmitting data over an HDSL2 loop. The present
invention is comprised of a direct sequence (DS) transmitter 10 and a
direct sequence receiver 12. The transmitter 10 is operable to provide an
output to a hybrid circuit 14 which interfaces with an HDSL2 loop 16. The
hybrid 14 is operable to extract received information therefrom and input
it to the receiver 12.
The data input is first input through a scrambler 18, the output thereof
input to the DS transmitter 10 and, similarly, the output of the DS
receiver 12 is input into a descrambler 20, to provide a data output. The
DS transmitter 10 has the input thereof input through a trellis encoder
22. The trellis encoder 22 allows the system to use trellis coded
modulation and precoding which will allow for higher margins to be
achieved without excessive latency, this being a standard system. The
output of the trellis encoder 22 is input to a mapping block 24 to provide
a bit-to-level mapping and then to a precoder 26. This output is then
provided to a transmitter block 28 which is operable to shape the spectrum
and also drive the loop 16 via the hybrid 14.
By comparison, the DS receiver 12 is comprised of an input receive block
30, which is operable to receive the information from the hybrid 14, this
having a typical response that will be described hereinbelow. The output
of the receive block 30 is input to a summing block 32 which is operable
to provide for some echo-cancellation. This is facilitated with the use of
an adaptive echo-canceler block 34 which has the input thereof connected
to the output of the precoder 26 and the DS transmitter 10. This provides
an error signal on the output of canceler block 34 which is subtracted
from the receive output from block 30. This provides for some
echo-cancellation, this not being the subject of the present invention
and, therefore, will not be discussed. The output of the block 32 is input
to an adaptive feed forward equalizer 36, which then provides an output to
a trellis decoder for the precoded channel in a block 38. This provides
the decoded output signal, which is then input to the descrambler 20.
In prior art systems, the above-noted system of FIG. 1 is utilized with a
baud rate of 1.03467 MHz for the DS transmitter 10 with a receive baud
rate at the same frequency. In one prior art system, the POET-PAM
(partially overlapped echo-cancel transmission pulse amplitude modulation)
system described in the Schneider reference, which was incorporated herein
by reference, and the system utilizes non-symmetrical baud rates to
achieve self crosstalk reduction. In prior art systems, the transmitter
has a defined specification which is set forth in Table 1.
TABLE 1
______________________________________
POET-PAM Transmitter Specification
DS Transmitter: located in CO
US Transmitter: located in RT
______________________________________
Transmit 9.7 dBm Transmit 14.7 dBm
Power: Power:
Max PSD: -44.0 dBm/Hz Max PSD: -38.0 dBm/Hz
PSD: See FIG. 3 PSD: See FIG. 2
Baud Rate:
1.0347 MHz Baud Rate:
620.8 Khz
Constellation
2 bits/dimension
Constellation
3 bits/dimension
Size: Size:
Information
1.5 bits/ Information
2.5 bits/
Rate: dimension Rate: dimension
______________________________________
Associated with this system will be a transmitter power spectral density.
Additionally, there are provided various transmit templates for the
upstream and downstream transmitter power spectral densities.
To successfully improve the performance in accordance with the various
benchmarks that are provided, various papers have come out with specific
templates for providing a very high uncoded SNR margin in excess of 1 dB
such that additional coding techniques can be utilized to provide for
forward error correction to improve the coded performance margin on CSA
loops. One technique for providing a template is described in M. Rude,
"Refined HDSL2 Transmission Masks: Performance & Compatibility," ADC
Telecommunications, which is incorporated herein by reference. In this
Rude reference, the transmit power spectral density for both the upstream
and downstream are referred to as transmit masks. In this reference, they
are provided by the following Table 2 definition.
TABLE 2
______________________________________
Transmit PSDs in Piecewise Linear Form
______________________________________
HDSL2 Upstream
Frequency [kHz]
0.1 25 200 205 295 315 600
PSD Level -63.1 -38.1 -38.1
-33.1
-33.1
-120.1
-120.1
[dBm/Hz]
HDSL2 Downstream
Frequency [kHz]
0.1 25 200 205 290 295 600
PSD Level -68.1 -39.1 -39.1
-47.1
-47.1
-57.1 -57.1
[dBm/Hz]
______________________________________
These particular masks have been purported to illustrate full CSA reach
with 6 dB margin in HDSL2 without degrading the existing services. This
performance is facilitated by boosting the upstream PSD in a region where
it causes the least interference.
In another technique, set forth in G. Zimmerman, "Performance of Spectral
Compatibility Comparison of POET-PAM and OverCAPped Transmissions for
HDSL2," distributed to T1E1.4 Technical Subcommittee Working Group Members
on May 15, 1997, there are illustrated upstream and downstream transmit
spectra, which reference is incorporated herein by reference. In this
reference, there is illustrated an upstream transmit spectra that was
relatively constant from zero to 300 kHz and falls off to -60 dB, and then
at 350 kHz falls off to -110 dB, and then decays therefrom. Downstream
transmit spectra was held relatively constant at -45 dB to approximately
300 kHz, and then falls off to -60 dB and was held constant up to
approximately 575 kHz, and then falls off to -90 dB in a relatively sharp
response. This exhibited some improvement, but still fell short.
Referring now to FIG. 2, there is illustrated a template for the OPTIS
HDSL2 transmission spectra. The OPTIS system for a symmetric PAM
transmission with a nominal information rate of 3 bits/dimension to
transport 1.552.times.10.sup.6 bits/sec. As such, the nominal symbol rate
for the upstream and downstream directions is 517,333 symbols/sec. In FIG.
3, the PSD templates are shown for the upstream in solid and the
downstream in phantom. These indicate the break points for the upstream
and downstream PSDs, respectively. It can be seen that at approximately
175 kHz, the PSD increases from -40 dBm-Hz to 35 dBm-Hz. This response is
flat up to approximately 250 kHz, at which time it falls very sharply to
approximately -82 dBm-Hz. It then falls off to -105 dBm-Hz at 400 kHz, and
then decreases at a slower rate. By comparison, the downstream transmit
spectrum begins to decrease at 175 kHz to -45 dBm-Hz at approximately 260
kHz. It then increases to approximately -37 dBm-Hz very sharply and
remains there until approximately 400 kHz, at which time it begins to fall
off fairly sharply to -72 dBm-Hz, and then falls off very slowly after
that.
Referring now to FIG. 3, there is illustrated the PSD templates for both
the downstream and the upstream templates for the present invention. In
the present invention, the downstream and upstream templates are divided
into three regions, a first region 40, a second region 42, and a third
region 44. The first region 40 is referred to as the "full-duplex" region
wherein energy is present for both the upstream and the downstream. The
regions 42 and 44 are both referred to as "half-duplex" regions since in
the region 42, the power in that region is substantially the downstream
power, and in the region 44, the power is substantially the upstream
power. It is the existence of these two half-duplex regions that improves
performance, as will be described hereinbelow with respect to specific
examples. The region 40 extends from approximately 0 kHz to approximately
175 kHz. The region 42 extends from 175 kHz to approximately 260 kHz.
Region 44 extends from 260 kHz to 350 kHz. However, it is noted that the
response of each of the templates is illustrated in a "brick-wall"
configuration; however, it should be understood that achieving a
brick-wall response is difficult at best. As such, the sharp lines are for
illustrative purpose only, and they merely show that the rejection is very
sharp.
The region 40 illustrates the upstream is increased from 0 kHz to a level
of 35 dBm-Hz at approximately 40 kHz, and then remaining flat up to
approximately 175 kHz, at which time it falls off very sharply at the
border of regions 40 and 42. By comparison, the downstream PSD rises to
approximately -38 dBm-Hz and remains there until 175 kHz, at which time it
rises to a level of approximately -32 dBm-Hz at the border of the two
regions 40 and 42. It remains at this level for all of region 42, at which
time it falls very sharply at the border between regions 42 and 44. At the
border between regions 42 and 44, the upstream PSD increases very rapidly
to a level of -32 dBm-Hz and remains there up to the "roll-off" point of
approximately 350 kHz, at which time it will flow very quickly in a sharp
filter response. It is noted that the response below -60 dBm-Hz is not
illustrated. Also, the levels of the downstream and upstream PSDs in
regions 42 and 44 are substantially equal. However, they could be slightly
different. It is important to note that the half-duplex operation for
regions 42 and 44 results in a separation of power densities and,
therefore, it is believed that this does add to the improvement in the
SNR.
The upstream and downstream spectra for a twisted pair utilizing HDSL2
relates to the actual filtered spectra output by the upstream transmitter
to the downstream transmitter. Typically, the upstream location is defined
as the central office, whereas the subscriber is defined as the downstream
location. The upstream spectra, therefore, relates to transmission from
the subscriber to the central office, and the downstream spectra relates
to transmissions from the central office to the subscriber. Therefore, it
can be seen that information for both the upstream and downstream
transmissions is transmitted in the first region 40. However, none of the
information transmitted in region 42 will be received with the upstream
transmissions, i.e., they will not be received by the central office.
Similarly, any information transmitted from the central office to the
subscriber will not see any of the information in region 44.
Of importance is the border between regions 42 and 44. This is at a
frequency of 250 KHz, which is equal to f.sub.baud /2. This is at a point
48 on the spectra of FIG. 3. The transmission is a PAM transmission which
utilizes frequency division multiplexing (FDM). The signal-to-noise ratio
(SNR) folds at f.sub.baud /2 for PAM, at point 48. When calculating SNR,
the margins for PAM are computed utilizing an optimal view of the
calculations in accordance with the following equation:
##EQU1##
where fSNR(f) is the folded received signal-to-noise ration, defined as:
##EQU2##
and S(f) is the desired HDSL2 signal's transmit power spectral density,
.vertline.H(f).vertline..sup.2 is the magnitude squared of the wireline
loop transfer function, and N(f) is the total noise power spectral density
(crosstalk+background noise) computed as described above. The SNR folding
is calculated up to three times the Nyquist rate.
In general, the region 42 associated with the downstream and the region 44
associated with the upstream could be reversed such that the upstream were
in region 42 and the downstream were in region 44. Further, the width of
these regions and the relative amplitudes can be varied, although the
optimal configuration is illustrated in FIG. 3. Therefore, regions 42 and
44 could be narrower and could be reversed, it being only important that
there is a substantial rejection of one or the other of the upstream or
downstream energy within that particular portion of the spectra. Further,
it is also important that these be substantially symmetrical about
F.sub.baud /2.
Uncoded optimal-DSE performance for the above-noted PSDs in FIG. 3 are
provided as compared to the OPTIS system in Table 3. Three performances
are particularly noteworthy. First, the worst case margin for the present
system which is labeled "MONET-PAM" over loops 4 and 6 and all disturbers
is greater than 2 dB. Second, the self next+fext margin is greater than 6
dB over loops 4 and 6. Finally, the MONET-PAM provides higher margins than
OPTIS in all cases.
TABLE 3
__________________________________________________________________________
Uncoded, Optimal-DFE Performance/Service Margins
OPTIS MONET-PAM
HDSL2 Performance
Loop 6
Loop 4
Loop 6
Loop 4
Crosstalk Source
Service
Up Dn Up Dn Up Dn Up Dn dif*
__________________________________________________________________________
39 EC ADSL HDSL2
2.68
16.2
1.62
17.0
3.12
12.5
2.37
12.2
.75
49 FDM ADSL HDSL2
8.77
15.7
7.50
16.5
9.20
11.9
8.23
11.7
.73
49 HDSL HDSL2
3.06
14.5
2.00
12.6
9.38
3.14
8.60
2.08
0.1
39 Self* HDSL2
2.95
12.5
1.89
13.3
10.3
6.03
10.6
6.31
4.1
25 T1 HDSL2
20.3
16.7
19.2
15.7
19.8
20.3
19.0
19.3
3.3
24 T1 + 24 Self
HDSL2
5.15
1.78
4.09
0.90
7.15
5.01
6.39
4.08
3.2
24 FDM ADSL + 24 HDSL
HDSL2
2.36
12.1
1.28
12.0
3.05
4.46
2.28
3.40
1.0
29 Self + 10 HDSL + 10 T1
HDSL2
2.89
1.64
1.83
0.68
6.62
3.35
5.90
2.38
1.7
29 Self + 10 HDSL + 10 EC
HDSL2
1.73
11.3
0.67
11.7
3.68
3.33
2.75
2.56
2.1
__________________________________________________________________________
dif* difference between worstcase MONETPAM and worstcase OPTIS.
Self* HDSL2 self NEXT + self FEXT
Margins for ADSL and HDSL with the system of the present invention, and by
comparison to the OPTIS system, are presented in Table 4. As with
performance margin, the present system provides higher margins than OPTIS
in all cases. Most notably, the margin into EC ADSL is 1.5 dB higher, and
the margin into FDM ADSL is more than 2 dB higher.
TABLE 4
______________________________________
Spectral-Compatibility Margins
HDSL2
Performance OPTIS MONET-PAM
Crosstalk Loop 6 Loop 4 Loop 6
Loop 4
Source Service Up Dn Up Dn Up Dn Up Dn dif*
______________________________________
49 HDSL HDSL 8.53 8.09 8.53 8.09
39 HDSL2
HDSL 8.34 7.96 10.1 10.9 .03
upstream
39 HDSL2
HDSL 10.2 9.78 8.28 7.99
downstream
39 HDSL EC ADSL 8.43 9.55 8.43 9.55
39 HDSL2
EC ADSL 8.19 10.5 9.70 11.7 1.5
49 HDSL EC ADSL 8.12 9.24 8.12 9.24
49 HDSL2
EC ADSL 7.98 10.3 9.59 11.6 1.6
49 HDSL FDM ADSL 6.01 7.32 6.01 7.32
39 HDSL FDM ADSL 6.08 8.70 8.22 10.4 2.1
______________________________________
dif* difference between worstcase MONETPAM and worstcase OPTIS.
One of the key objectives in measuring performance margins with the system
of the present invention has been to match the modeling/simulation
conditions utilized in other T1E1.4 contributions as closely as possible.
The simulation conditions for generating the simulation data is noted in
Table 5.
TABLE 5
______________________________________
Simulation Conditions
______________________________________
500 Hz rectangular-rule integration
MONET-PAN spectra linearly inter-
Lagrange-interpolated loop
polated from (2 .multidot. 1552)/3 Hz sampled
parameters, PIC 70C loops
data
Optimistic mixed-crosstalk NEXT
NEXT coupling model: 2-piece
summing, pessimistic FEXT
Unger model
summing Required SNR margin for 1e-7 BER:
Margin calculated with T/3 FFE,
27.7 dB
per T1E1.4/97-180R1, section
-140 dBm/Hz noise floor
5.4.2.2.1.1 135 Ohm source/load impedance
Spectral models as in Annex B of
PAM line-transformer hpf corner@
T1.413-1995, (0.025-fbaud)/2
with exceptions as in
T1E1.4/97-237, p.4.
______________________________________
The MONET-PAM system of the present invention provide spectra that share
many attributes with other proposed spectra. In particular, it assumes the
same data rate (1.552 Mb/s), line code (3 bit-per-symbol PAM), and
low-frequency, highpass corner shape as OPTIS. Also like OPTIS, MONET-PAM
employs a mix of FDM (Frequency-Domain Multiplexed) and FDX (Full-Duplex)
spectral shaping between the upstream and downstream spectra. A plot of
the ideal spectra template is illustrated in FIG. 3, as described
hereinabove. A list of key attributes for MONET-PAM is given in Table 6.
However, MONET-PAM differs from OPTIS in key respects. For example, both
the upstream and downstream templates have boosted regions, and the
boosted regions are FDM. Also, the boosted regions are symmetric about
fbaud/2. Given the parameters and constraints given to the optimization
program, there are no better spectra.
TABLE 6
______________________________________
Key Attributes of MONET-PAM HDSL2
______________________________________
PAM w/3 bits/symbol
fbaud:
517.333. . .symbols/s
fbit: 1.552e6 bits/s
Low-frequency highpass corner: 15% excess-bandwidth
square-root raised-cosine
Upstream transmit power:
20.14 dBm Downstream
18.76 dBm
transmit
power:
Upstream FDX power:
-35 dBm/Hz
Downstream
-39 dBm/Hz
FDX power:
Upstream FDM power
-32 Downstream
-32
FDM power:
First bandedge:
170 kHz
Second bandedge:
258.666. . .
Third bandedge:
347.333. . .
______________________________________
In summary, there has been provided an improved PSD template for an HDSL2
loop transmission system which utilizes a system that divides the upstream
and downstream spectra into three regions, a full-duplex region and two
half-duplex regions. In the full-duplex region, the prior spectral density
of the upstream and downstream systems is substantially similar with
energy being present in region 1 for both the upstream and the downstream.
In the half-duplex regions, the power density in those regions is
substantially either the upstream or the downstream. Each of these regions
is very sharply defined with the power structure density substantially the
same for each of the half-duplex regions.
Although the preferred embodiment has been described in detail, it should
be understood that various changes, substitutions and alterations can be
made therein without departing from the spirit and scope of the invention
as defined by the appended claims.
Top